The present invention relates to a mechanical device to link a payload and a parachute together prior to and during the parachute dropping of the payload, and to effect automatic separation of the payload from the parachute after the payload and parachute have landed in a target area, particularly on water.
Pyrotechnic marine markers and sonobuoys are used by armed forces and civilian organizations for a variety of purpose such as reference marking, signalling, wind-drift indicating, tracking in anti-submarine warfare, search and rescue operations and paratroop and airdrop operations. Because of the nature of these operations, it is imperative that the marking devices perform reliably and effectively.
A controlling factor in marker design and in their operation while floating on water is the effect of impact they receive upon landing. As they can be deployed from a variety of delivery flight envelopes, with altitudes ranging from 0-3000 m and release speeds ranging from hover to 300 knots, severe damage can result if a poor (i.e. violent) impact with water is made. To ensure a correct landing attitude for all possible delivery modes, it is desirable to equip the marker with a parachute or even more simply a drag-chute or dragribbon. While not all of these latter will substantially reduce the rate of descent of a marker, they all serve the purpose of orientating the marker correctly so that it makes a streamlined entry into the water with no resultant damage. Once on the water's surface, however, a complication arises in that the parachute (hereafter "parachute" will be intended also to include drag-chutes and drag-ribbons) will be carried by the waves and will tend to pull at the marker during its functioning. This dragging action will periodically submerge or swamp the marker, severely limiting its performance.
Clearly a method of separating the payload (i.e. marker) from its parachute immediately upon touchdown is required. The problem is not restricted solely to the deployment of signalling markers as described above. Other manoeuvres, such as air or ground towing and the slinging of loads from helicopters, have requirements for the automatic separation of a tow line from a payload.
There have been relatively few methods or devices developed to solve the problem of parachute/payload separation. Perhaps the most widely used method today relates to the use of "cable cutters". These consist of small explosive charges, usually in the form of detonators that are fired electrically to either directly sever a cable or cause a sharp cutting object to impact against and rupture the cable.
Alternatively, different types of tension links have been developed for parachute release which are either electrically or electronically activated. Almost exclusively, however, automatic parachute/payload separation has been carried out to the present by means of devices containing explosive cable cutters, electronic timing circuits, electronic remote control circuits or salt-water battery circuits.
While such devices may work reliably and be advantageous for certain fields of application, they do possess drawbacks that could limit their use in other areas. Of foremost importance is the explosive contained in the cable cutters. The presence of explosive material imposes limitations or at a minimum necessitates specific procedures for the storage, handling and use of the entire device. In certain circumstances this may unduly complicate the comparative ease with which the device could otherwise be employed.
Both the cable cutter and the electrically activated tension link require reliable and failsafe firing circuits, with the needed electrical energy to be provided either by adequate self-contained batteries or by external sources. If the circuit is designed to be fired automatically, it must do so only after a well-defined event or series of events or time lapse. Remote firing requires that the circuit be adequately shielded from stray triggering pulses. In either case, and with manual firing, the circuit may be required to remain serviceable after extended periods of storage or upon storage under arduous environmental conditions.
Depending on the type of payload in question, such a system may be both complicated and costly. For marine markers where the tension link must be self-activating and "disposable", a low cost is essentially a prerequisite. The costs involved in a reliable electrical firing circuit or with explosive cutters makes their use rather unattractive with relatively small, low-cost payloads.
Thus, it is an object of the present invention to provide a mechanical tension link which is designed primarily to carry out automatic separation of a payload from its parachute following touchdown without the use of explosive charges or electrical or electronic activation devices. It is a related object of the present invention to provide a tension link consisting uniquely of mechanical components and which is self-activating to separate the payload from its parachute on touchdown, requiring no external human, explosive or electronic impetus to bring about its function.